Long-term growth and subsidence of Ascension Island: Constraints on the rheology of young oceanic lithosphere

Details Long-term growth and subsidence of Ascension Island: Constraints on the rheology of young oceanic lithosphere Long-term growth and subsidence of Ascension Island: Constraints on the rheology of young oceanic lithosphere

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010georl..3723306m&link_type=abstract

Geophysical Research Letters, Volume 37, Issue 23, CiteID L23306

Physics

Geophysics

Tectonophysics: Lithospheric Flexure, Structural Geology: Rheology: Crust And Lithosphere (8159), Marine Geology And Geophysics: Oceanic Hotspots And Intraplate Volcanism, Marine Geology And Geophysics: Gravity And Isostasy (1218, 1222), Mineralogy And Petrology: Intra-Plate Processes (1033, 8415)

Scientific paper

The dating of material from deep boreholes drilled in volcanic ocean islands allows constraints to be placed on their growth and long-term subsidence rates. We dated lavas from a 3 km geothermal borehole at Ascension Island by the laser-heating 40Ar/39Ar technique. The samples yield ages of up to 3.4 Ma and volcanic growth rates of ˜0.4 km/Myr. The transition from submarine to subaerial eruption occurs at ˜710 m below present sea level and 2.5 Ma. Since 2.5 Ma, there has been ˜430-500 m of subsidence over and above the expected ˜190-260 m due to lithospheric cooling. Plausible elastic thicknesses and growth histories would generate a maximum elastic subsidence since 2.5 Ma of ˜200 m. We infer that the subsidence includes a component of viscous relaxation resulting from rapid loading prior to 2.5 Ma, and place constraints on the timescale of this relaxation, and hence the viscosity of the underlying lithosphere.

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